This project concerns the elucidation of the function and the biological importance of human serum and secretory immunoglobulins, with particular emphasis on IgA, in the regulation of immunological responsiveness to environmental food and microbial antigens. Serum and secretory immune responses induced by oral immunization with such environmental antigens will be measured at both humoral and cellular levels. The influence of preexisting serum and secretory antibodies on the absorption of ubiquitous and unusual environmental antigens, and on the presence and fate of immune complexes in the circulation will be measured and correlated with the immune response induced after the ingestion of such antigens. The overall aim and long term goal of these studies are to elucidate the role of secretory and serum antibodies in the regulation of the immune response to environmental antigens encounted through the mucosal route. The studies will also yield basic information that may facilitate the development of novel orally-administered vaccines designed for the selective induction of antibodies in external secretions, which protect large surface areas of mucous membranes - the most common portals of entry of infectious agents and environmental antigens.